Telephone-exchange.



. PATENTED AUG. 1, 1905. HIG. WEBSTER. TELEPHONE EXCHANGE.APPLIGATIGNIPILED gov, 16, 1904.

SBHEETS-SHEET 1.

PATENTED AUG. 1, 1905 H. G. WEBSTER TELEPHONE EXCHANGE.

APPLICATION rmm NOV.16, 1904.

a sums-Exam z.

I M C Amamv n nm limwnfmumamnkhm mama No. 795,872 I PATENTED AUG. 1,1905. H. G. WEBSTER.

TELEPHONE EXCHANGE.

APPLICATION FILED NOV. 16, 1904.

3 BHEETBSHEET 3.

7? j 1 1.5 a WITNESSES: INVENTOA.

UNITED STATES PATENT OFFICE.

HARRY G. WEBSTEIL OF CHICAGO, ILLINOIS, ASSIGNOR TO MILO G. KELLOGG, OFCHICAGO, ILLINOIS.

TELEPHONE-EXCHANGE.

Specification of Letters Patent.

Patented Aug. 1, 1905.,

To ctZZ whom it may concern:

Be it known that I, HARRY G. WEBSTER, a citizen of the United States,and a resident of Chicago, county of Cook, and State of Illinois, haveinvented a certain new and useful Improvement in Telephone-ExchangeSystems, of which the following is a full, clear, concise, and exactdescription.

My invention relates to telephone-exchange systems employing a centralbattery for signaling, and particularly to that type adapted forcentralbattery transmission, in which the switching-terminals orspring-jacks of the lines are constructed each with only twocontact-pieces connected with the two line con-- d uetors respectively,the connecting-plugs being correspondingly provided each with only twocontacts, these forming the terminals of link conductors by which linesare temporarily switched together.

The principal object of my invention is to provide improved means forcontrolling the display of the subscribers calling-signal and theconnections of the talking-circuit, a second object being the provisionof improved means for securing a positive busy test.

Other objects and advantages of my invention will be apparent to thoseskilled in the art from the following description.

In accordance, with my invention I associate with the line-circuit asignal-controlling electromagnet, the signal being normally under thecontrol of the subscriber, whereby a call may be initiated at thecentral ofiiee. A second electromagnet normally under the corn trol ofthe exchange operator is also associated with the line-circuit, adaptedwhen actuated to destroy the substation control of the said signal andto change the normal circuit of the line to one adapted for thesatisfactory transmission of speech. This electromagnet and itsassociated mechanism may be in the form of a relay-magnet and will forconvenience be hereinafter referred to as the cutofl relay. The windingsof this relay are divided into two portions, which may be of equal ordifferent energizing capacities, and connected cumulatively with respectto their effect upon the magnet or may be of unequal energizing capacityand connected differentially with respect to their effect upon themagnet. In its preferred form the two portions are arranged uponopposite ends of the magnet-core, although I have indicated amodification in which they may be twin windings or superimposedwindings.

In the preferred embodiment of my invention that portion of oneline-limb extending to the substation is connected to the intermediatepoint of the winding or windings, one portion of the windings beingconnected directly to the return side of the central batteryand theother portion being normally in cluded in that portion of the line-limbextending to the switching-terminals. A normal earth connection isprovided for the intermediate point of the windings of a characteradapted to substantially short-circuit that portion of the windingswhich is connected to the return side of the battery and to preventextraneous currents upon the line-limb from altering theelectricalcondition of the associated contacts of theswitching-terminals.

The signal-controlling electromagnet above referred to may be in theform of a magnet controlling a mechanical signal or may be arelay-magnet controlling a signal in a local circuit, such as anincandescent lamp, and the display of this signal may be preventedeither by opening its local circuit or by opening the circuit of theelectromagnet or by a locking-winding adapted to prevent such display orby other obvious means well known to those skilled in the art, and I donot wish to be limited to any specific arrangement of magnet and signalor means by which the display of the signal is prevented.

Cord connecting apparatus is provided adapted upon the insertion of itsconnectingplug into a switching-terminal to complete a battery-circuitwhich includes that portion of the relay-windings normallyin circuitwith a contact of the switching-terminal. The cutoff relay being thusenergized, its actuation will destroy the substation control of thecalling-signal, as above referred to. Further-' more, the actuation ofthe cut-off relay operates to disconnect the aforesaid normal earthconnection, thus removing the short circuit from that portion of thewindings associated with the return side of the battery, bringing saidportion into branch circuit of the line, and to connect the associatedline-limb directly to its corresponding contact of theswitching-terminal. This direct connection may be accomplished either byshort-circuiting the first-mentioned portion of the windings or byconnecting the line-limb directly to its wire leading to theswitching-terminal and openingthe circuit of said portion. While I havereferred to this relay as having a winding or windings, it will beunderstood that the two terms are used interchangeably and that therelay has actually a winding which is normally continuous, although aportion of this winding may be normally shortcircuited or maybesubsequently divided into two portions, or one portion of the windingmay be connected difierentially with respect to the other, and thisexplanation is made for the sake of clearness and to avoid limitingmyself unnecessarily, inasmuch as the two portions ofthe winding will behereinafter referred to as different windings for the sake of brevity.

I will describe my invention more fully by reference to the accompanyingdrawings, forming a part of this specification, in which Figure 1illustrates two complete line-circuits together with appropriate cordconnecting apparatus, all organized in accordance with the preferredform of my invention. Figs. 2 and 3 illustrate alternative cordconnecting structures adapted for use with the line-circuit arrangementof Fig. 1. Fig. 1 illustrates a modification of the line-circuitarrangement of Fig. 1 in which the relay-winding associated with theswitching-terminal is disconnected after the operation of the relay.Fig. 5 illustrates another modification of the linecireuit arrangementof my invention, and Fig. 6 is adiagram indicating cord connectingapparatus adapted to cooperate with the structure of Fig. 5. Figs. 7, 8,and 9 illustrate further modifications of the line-circuit of myinvention, and Figs. 10 and 11 illustrate an additional modificationwith appropriate cord connecting apparatus.

Like characters refer to like parts in the various figures.

Referring first to Fig. 1, the subscribers apparatus is represented asconsisting of a telephone-hook switch IL, signal-bell 6, condenser 0,transmitter If, and receiver '2', the bell and condenser being inpermanent bridge of the two line-limbs and the receiver and transmitterbeing in a normally open circuit, which is closed upon the elevation ofthe switch-hook. Although I have shown but one arrangement, it will beunderstood by those skilled in the art that various other ar-.

rangements of the subscribers apparatus may be used, and 1 do notconfine myself to the particular arrangement illustrated. Under normalconditions the receiver being upon its switch-hook the condenser cprevents a normal flow of current from the battery C at the centraloffice over the telephone-line. WVhen, however, the subscriber removeshis telephone from its hook, thus establishing a relatively lowresistance path for the flow of cur rent through the transmitter 25 andreceiver a, the signal-controlling relay 1 at the central the saidbattery C.

ofiice will be energized by the fiow of current from the said batterythrough the winding of relay 4, anvil 50, and armature 9 of the cut-offrelay 3; over limb 1 of the telephoneline, through the substation, backto the central ofiice over limb 2, through armature 8 and anvil 51 ofrelay 3 to the return side of This energization of relay 4 closes thelocal circuit of the callinglamp 5, causing its illumination andindicating to the operator that the subscriber has removed his telephonefrom its hook for the purpose of makinga call. It will be noticed thatwinding 7 of relay 3 is at this time shortcircuited by the contactbetween anvil 51 and armature 8 and that winding 6 .is included in thecircuit of the line-limb, which normally stands open at the sleevecontact-piece of the spring-jacks 10. Each subscribers line is providedwith one or more spring-jacks, each having contact-pieces connectedthereto, and each operator is provided with cord-circuits adapted tounite the lines for conversation. On observing the calling-signal theoperator will insert the left-hand or answering plug P of thecord-circuit into a spring-jack of the causing the tip and sleevecontact-pieces of the plug to engage, respectively, with correspondingcontact-pieces of the spring-jack. The sleeve contact pieces of the plugand spring-jack complete a new circuit for the flow of current frombattery 0, which may be traced as follows: through conductor 52, winding20 of relay 16, strand 14:, wire 53, winding 6 of relay 3, armature 8,and anvil 51 to the grounded pole of the battery. This flow of currentwill cause the operation of relay 3, causing it to break the normalcircuit of relay 4 at anvil 50 and armature 9, thereby extinguishing thecalling lamp 5. Also the attraction of armature 8 first disengages anvil51, thus removing the short circuit from winding 7 of the relay 3 andallowing its energizing-current to now flow through both windings. Thecontinued attraction of armature 8 causes it to engage anvil 11, thusshort-circuiting winding 6; but the current which now flows throughwinding 7 maintains the energization of the relay as long as the plug Pis in the spring-jack. Under normal conditions namely, when the receiverat the substation is upon its switchhookthe current which flows over thepath including winding 20 of relay 16, which is armature 24, andconductor 54 to the grounded pole of the battery. The current-flow atthis time is therefore limited by the resistance of the windings of therelay 3. When the receiver is removed from its switch-hook, another pathfor current-flow through winding 20 is thus established, which includeslimbs 1 and 2 of the line, the substation receiver and transmitter, tipcontact-pieces of the spring-jack and plug, strand 12, winding 18 ofrelay 16, and conductor 54, which is connected to the grounded pole ofthe battery G. The increased energization of relay 16 due to theincrease in current through winding 20 or to the energizing effect ofthe current through winding 18, or to both, causes the furtherattraction of armature 24L, breaking the circuit of lamp 22 at anvil 28and spring 26, causing the extinguishment'ot the lamp. Condensers (Z dunite strands 12 and 13 and strands 14 and 15 of the cord-circuit,allowing the operator to converse with the calling subscriber at thistime and to allow conversation between the two subscribers when theconnection has been established. The operator actuates her listening-keylevers it 7:, thus cutting her telephone S into the conversationcircuit,and having determined from the calling subscriber the number of thesubscriber desired, as L, touches the tip contact-piece of theright-hand or calling plug 0 to the sleeve contact-piece, which alsoconstitutes a testing-terminal of the spring-jack of the line wanted. Itthe line be busy, this testing-terminal will have a potential differentfrom that of the ground or common terminal of the battery C, and a flowof current will result from said battery to tipstrands 13 throughwinding 19 of relay 17 and thence by conductor 54 to the return side ofbattery G in the well-known-manner. This flow of current will alter thepotential at the terminals of condenser c, and thereby cause the clickin the operators receiver, which indicates that the line is busy.Should,however,the desired line be idle, the testing-terminal of theline will be at the potential of the earth or return pole of the battery(I regardless of any extraneous currents or disturbances upon theline-limbs on account of the normally closed contact between armature 8and anvil 51 of relay 3. It will be well understood that this normalconnection completesa circuit from the centraloffice ground at battery Cto that side of winding 6 which is connected to limb 2, and therebynormally short-circuits any current which might be present in theoutside wire of limb 2 and prevents such current from altering thenormal electrical condition of the sleeve contactpieces ortesting-terminals associated with that line-limb. Under this normalcondition the testing-terminal and plug-tip would be at the samepotential and no current will flow when they are brought in contact.

The operator would thus hear no click, would know that the "lesired linewas idle, would insert the rightiand plug 0 into the spring-jack of thedesired line, and actuate the ringing-key levers g g to include thecalling-generator G in circuit with the calling-bell b at thesubscribers station, thus causing the desired subscribers-bell to ring.During the actuation of the ringingkey levers relay 3 is energized bycurrent from battery D, through resistance 43 and strand 15, in a mannerthe same as in case of the insertion of the answering-plug alreadydescribed. Upon the restoration of the ringing-key the circuit isestablished through winding 21 of relay 17 and through relay 3 similarto those described with relation to relay 16, the relays 17 and '3operating in a manner similar to that already described in connectionwith the line of subscriber A. Both subscribers are now in conversationwith each other through the cord-strands 12 13 and 1a 15, which includethe condensers d cl, their transmitters being energized by current frombattery C through the windings of relays 16 and 17 over their respectiveline-circuits. In this system the windings of relays 16 and 17 are ofcomparatively low resistance compared with the resistance of winding 7of relays 3, thus providing for the proper distribution of thetalking-current. As soon as either subscriber replaces his telephoneupon its hook the corresponding relay 16 or 17 is partially deenergized,thus allowing the completion of the circuit of lamp 22 or. 23 by meansof the engagement of spring 26 or 27 with its corresponding anvil,causing the illumination of the lamp. When both subscribers havereplaced their telephones upon their hooks, both of the said supervisorylamps will be illuminated, thus indicating to the operator thatdisconnection is desired. Upon withdrawing the plugs from thespring-jacks the interruption of all current through relays 16 and 17andtheir consequent complete deenergization al-' lows their armatures toreturn to their normal positions, extinguishing both lamps. While relays3 are indicated as having two armatures 8 and 9, it will be understoodin this and thefollowing drawings that the relayarmatu res and theirassociated contacts or anvils are simply diagrammatic illustrations ofthe switching mechanism controlled by the relay-magnet and do not referto any particular mechanical construction. It will be understood bythose skilled in the artthat the switch- -ing mechanism of the relaymight be controlled by a single armature or two armatures or in anyother convenient manner and that this is also true of the diagrammaticillustration of relays 16 and 17 in the cord-circuit.

In Fig. 2 is indicated cord connecting apparatus adapted for associationwith the linecircuit apparatus of Fig. 1, differing from that previouslydescribed in that the circuits of the supervisory lamps are controlledby two relays for each, lamp, rather than by a single relay adapted totwo separate degrees of energization, and differs also in thearrangement of the testingcircuit.

WV hen a subscriber, as that of line A, calls, the insertion of theanswering-plug P completes a circuit from battery 0 through relay 30,strand 14, conductor 53, and relay 3, causing relay3 to operate in themanner previously described in connection with Fig. 1. The energizationof relay 30 by current flowing through this circuit would cause theillumination of lamp 22 its associated sleeve-contact ortesting-terminal through strand 13, armature 55 of relay 31, and itsassociated anvil 56 to test-relay 34 and ground or office return. Relay34 being thus energized will complete a circuit of battery (1 throughwinding 35 of the operators ind uction-coil and produce the click whichindicates that the line is busy. The subscriber is called, as in Fig. 1,and the restoration of the ringing-key lever completes a circuit ofbattery C through relay 31, strand 15, conductor 55, and relay 3,causing the energization of both relays. Relay 3 operates in the mannerpreviously described and relay 31 operates to close the circuit of thesupervisory lam p 23 to disconnect the test-relay 34 at anvil 56 and tocomplete the circuit of strand 13 through the engagement of armature 55with anvil 57, this contact subsequently remaining closed as long as theplug O is in the springjack. When the called subscriber answers,

current then flows through the two line-limbs and substation apparatus,strand 13, and relay 33, energizing relay 33, which by its contactsopens the circuit of supervisory lamp 23, extinguishing it. The twosubscribers are now united for conversation as in the system of Fig. 1,current, however, being furnished to the transmitter of the callingsubscriber from battery U and to that of the called. su-bscriber frombattery C and the windings of relays 30, 31, 32, and 33 are ofcomparatively low resistance as compared with that of winding 7 of relay3 of the lines in order to secure the proper distribution of current.

Fig. 3 illustrates. another arrangement of cord connecting apparatusadapted for association with the line-circuit apparatus of Fig. 1 andditfers from that of Fig. 2 only in regard to the busy-test arrangementand in regard to the. battery connections of the cordrelays. When thiscord-circuit of Fig. 3 is associated with the line-circuit of Fig. 1,the winding of relay 32 and winding 7 of relay 3 of the line would bothbe of relatively low resistance, as compared with the windings of relay30 or 36, in order to secure the proper distribution of current to thesubstation-trans mitter. Upon the insertion of a plug a circuit frombattery G will be completed through relay 30 and through the windings ofrelay 3, causing the two relays to operate, as previously described; butwhen the subscriber removes his receiver from its switch-hook currentwill then also flow from battery G through relay 32, the two line-limbs,and the substation apparatus, returning to the grounded side of thebattery C through winding '7 of relay 3. This is a case, therefore, inwhich the current which supplies the substationtransmitter is fed to theline through cordrelay 32 and a winding of the cut-ofl' relay 3 ratherthan through the two cord-relays. Referring to the busy test of thecord-circuit apparatus of this figure, it will be noticed that relay 33is normally disconnected from tipstrand 13 of the cord and that theoperators set S is provided with an induction-coil winding 35,constituting an earth connection for strand l3 and the operatorsreceiver. If the line tested is idle, its testing-terminal beingconnected directly to ground, no current will flow through this winding35; but if the line be busy the current will flow through strand 13,receiver 0', and winding 35 to ground, causing the customary click. Itwill be understood that this winding 35 may have suli'icient resistanceand impedance to prevent undue interference with any conversation whichmay be taking place in the circuit of a line tested, and this will alsohold good with regardto the winding of relay 34 in the cordcircuitarrangement of Fig. 2. \Vhen the plug O of Fig. 3 is inserted into thecalled line, a circuit for relay 36 being thus completed throughconductor 53 and the windings of relay 3 of the line, the action ofrelay 36 brings relay 33 into connection with strand 13 of the cord,maintaining this connection as long as the plug remains in the jack, andalso controls the circuit of the supervisory lamp in a manner similar torelay 30.

Fig. 4 indicates an alternative arrangement of the line-circuitapparatus of Fig. 1 and differs from it only in that winding 6 of relay3 is opened after being short-circuited, and the two windings of therelay may consequently in this arrangement be arranged concentricallyupon the magnet-core, if desired, rather than upon separate ends, asindicated in Fig. 1. W'hen the subscriber calls, the circuit of batteryC is completed, through relay 4, limb 1, transmitter and receiver, limb2, armature 39 and anvil 41, to the grounded or return side of thebattery, energizing relay 4 and causing the illumination of lamp 5. Uponthe insertion of a plug current being supplied to winding 6 throughconductor 53 causes the relay to operate as follows; Armature 39 firstdisengages anvil 41, thus allowing current to flow through winding 7 aswell, engages spring 40, thus short-circuiting winding 6, and the relaybeing now energized by current through winding 7 the final movement ofthe armature disengages armature 39 from spring 38, thus opening thecircuit of winding 6. The circuit of relay 4 has also been opened atarmature 9 and anvil 50 and the lamp extinguished, and a direct circuitnow exists between'limb 2 and the sleeve-contact of the jacks 10, whichincludes armature 39 and spring 40. The relay operates in a similarmanner when current is supplied to conductor 53 through the actuation ofthe ringing-key or when the operator plugs in to answer a subscriber, aswill be well understood from the previousdescriptions.

In Fig. 5 is illustrated a line-circuit arrangement embodying amodification of my invention, which differs from that of Fig. 1 in thatthe cut-off relay 3 has its windings associated with that line-limbwhich is connected to the tip contact-piece of the spring-jacks ratherthan the sleeve-contact and in that the sleeve contact-piece ortesting-terminal of the jacks is normally disconnected from thelinecircuit, and therefore does not require the normal ground connectionshown in Figs. 1 and 4.

Fig. 6 illustrates a cord-circuit arrangement adapted to cooperate withthe line-circuit arrangement of Fig. 5, and it is to be understood thatother cord-circuits are equally adaptable thereto. When a calling-plug Pis inserted into a jack 10, current flows from battery C, through relay45 and strand 12, through winding 6 of relay 3, to the return side ofthe battery, energizing both relays. The actuation of relay 3 breaks thenormal short circuit of winding 7 and then short-circuits windings 6, asin the other systems shown, and also disconnects the line-relay 4 fromthe line-limb and closes the circuit of limb 1 to the sleevecontact-pieces of the jacks 10. Current is now furnished to thesubscribers line through impedance-coil 44 and relay 32, thence throughlimb 1, and, the receiver being removed, through the substationapparatus, limb 2, and winding 7 of relay 3, and this current alsoserves to energize relay 3 as long as the receiver is removed from itsswitch-hook and the plug P remains in the spring-jack. The operator nowactuates her listening-key, obtains the number of the line. desired, andmakes the customary busy test. It will be observed that upon thedepression of the ringing-key lever 71: the circuit of relay 45 isopened at the upper contact of the lever and that if at this time theline tested is found to be busy current will flow through tip-strand 13,armature 47, and induction-coil winding 35 to ground, giving thecustomary click. When the operator releases her ringing-key and proceedsto call the desired subscriber, the circuit of relay 45 is againreestablished and armature 47 is brought into engagement with contact60, thus completing the circuit of strands 12 and 13, and armature 48,engaging its contact, completes the local circuit for the supervisorylamps 22 and 23. The

operation of relay 3 during the application of the calling-current tothe line will be readily understood from the foregoing descriptions, aswell as its operation by current flowing through relay 45 upon therestoration of the ringingkey. When the called subscriber answers,current is supplied to his line through the winding of relay 33, findingits path to the return side of the battery through winding 7 of relay 3,associated with that line, and the current through relays 32 or 33serves to control the circuit of the supervisory lamps in the well-knownmanner. The two subscribers are now connected for conversation, andtheir conversational circuit includes the condensers d in bridge of thewindings of relays 32 and 33, and current is furnished to the two linesthrough the impedance 44, which is common to both. If the operatoractuates her listening-key while conversation is in progress, theconnection between strands 12 and 13 will be broken at the upper contactof lever 70'; but the conversational circuit will then be maintained bythe condenser 46, as is readily apparent. It will also be understoodthat at this time relay 3 of the line called will have its energizationmaintained by current from battery C, through relay 45, contact 60,armature 47,

" and strand 13, and that relay 3, associated with the calling-line,will be energized by current flowing through relay 32 and the twoline-limbs. The resistance of relay-winding 45 is made relatively highin this arrange ment as compared with that of windings 7 and impedance44 in order to secure the proper distribution of current, and it will beunderstood that other means than the condensers 03 may be employed forpreventing the ordinary impedance of the windings of relays 32 and 33from interfering with the rapidly-alternating telephonic currents.

The line-circuit arrangement of Fig. 7 differs principally from that ofFig. 1, in. that thenormally open winding 6 of the relay 3 is associatedwith the opposite limb of the line from that with which the normallyshort-circuited winding 7 is connected. It also diflers in that thearrangement of relay-contacts is such that the normal connection ofarmature 8 with its anvil will be positively broken before thecorresponding connection of armature 9 is broken, as is indicated by thespring 72 and stop 73. This line-circuit arrangement is adapted forassociation with the cord-circuit arrangement of Fig. 2, and when soassociated .its operation is as follows: The subscriber A calls in theusual manner, completing a circuit of battery C through relay 4,contactspring 72, armature 9, limbs Land 2 of the line, anvil 74:, andarmature 8, to the ground 9 spring-jacks 10 and plug P, strand 12 andrelay 32, thence to the ground or common return of the exchange. Thiscurrent causes an initial movement of the relay armatures, which firstbrings armature 8 out of engagement with anvil 74, thus removing theshort circuit and allowing current from battery U to flow through relay30, strand 14:, the sleeve contact-pieces of the plug and spring-jack,through winding 7 of relay 3 to the return side of the battery. It willbe seen that at this time the spring 72 follows the movement of armature9 until it engages stop 7 3. The further actuation of the relay-contactsdisengages armature 9 from spring 7 2, causing it to engage anvil 7 5,thus short-circuiting winding 6, the relay then being wholly energizedby current through winding 7 and the subscribers transmitter beingenergized by current from battery C flowing through relays 30 and 32 ofthe cord-circuit. Incalling subscriber A the operator secures the busytest in the ordinary way, the sleeve contactpieces of the spring-jacks10 being normally at the potential of the central-office return, thepotential being raised upon the insertion of a connecting-plug bycurrent from battery C" or C through relay 30 or 31, as the case may be.In ringing the cut-off relay 3 is initially energized by current fromgenerator G through winding 6; but, as will be readily seen, after thisinitial energization current from battery l), through winding 7, willmaintain the energization during the process of ringing. After therestoration of the ringing-key current from battery C through relay 31,strand 15, anvil 7a, and armature 8 will cause the energization of relay31, completing the circuit of strand 13 at armature 55 and anvil 57,after which time the operation of the cut-off relay 3 will be the sameas described when the operator is answering a call. The operation of thesupervisory signals of the cord-circuit is the same as that previouslydescribed for Fig 2 and will be, therefore,

clearly understood.

The line-circuit arrangement of Fig. 8 differs from that of Fig. 7, inthat the normally open winding 6 of cut-ofl' relay 3 is associated withthe sleeve side of the line, and consequentl y with thetesting-terminalof the springjack, the normally short-circuited winding7 being connected with the opposite line-limb. It also differs in thatthe extinguishment of the line-lam p signal is secured byshort-circuiting the winding of linerelay 4 rather than by opening itscircuit. It is adapted for association with the cord-circuit arrangementof Fig. l; but when this cord-circuit is used in connection with Fig. 8the connections of the ringing-generator Gr should be similar to thoseindicated in Fig. 11, the ground being shifted to the tip side of thegenerator and the battery D being omitted. The protective resistance 43may or may not be employed, as desired. The subscriber calls, as usual,by removing his receiver, thus closing a circuit of battery C throughconductor 79, anvil 74, armature 8, relay 4:, limbs 1 and 2, armature 9,and spring 72 to the return side of the battery. Upon the insertion ofthe answering plug circuit is first completed from batteryO of Fig.1through conductor 52, winding 20 of relay 16, strand 14:, sleeve-contactot' the plug and spring-jack, winding 6, armature 9, and contact 72 tothe return side of the battery. This current causes an initial actuationof relay 3, and armature 8 first disengages anvil 74, thus bringingwinding7 into circuit. Current then flows from battery G of Fig. 8through winding 7, relay 4, limbs 1 and 2 of the line to the return sideof the battery and also through limb 1 to the tip contact-pieces of thespring-jacks 10, and thence to strand 12 and winding 18 of relay 16 tothe officereturn through conductor 54. The further movement of therelay-armatures causes armature 9 to disengage spring 72, thus breakingthe normal earth connection of limb 2 and to engage anvil 75, thusshort-circuiting winding 6. Armature 8 also at this time engages anvil76, thus short-circuiting the winding of relay 1 and extinguishing thecalling-lamp 5. Current is now supplied to the substationtransmitterthrough winding 20 of relay 16 in the cord-circuit and reaches thereturn side of the battery through winding 18 of the same relay, while acircuit for winding 7 is provided from battery C of Fig. 8 througharmature 8, anvil 76, strand 12 of the cord-circuit, and winding 18 ofthe relay 16. The relay 16 is thus fully energized and supervisory lamp22 not illuminated. When the subscriber replaces his receiver upon itsswitchhoolz, thus opening the circuit of limbs 1 and 2, the relay 16 isthen only energized by current flowing through the last-mentionedcircuit, and its contacts assume their intermediate position, causinglamp 22 to become lighted. In calling subscriber A the operator tests inthe usual way, the sleeve contactpieces of jacks 10 being normally atthe potential of the oflice-return, their potential being raised uponthe insertion of a connecting-plug. Upon the actuation of theringingkey, the generator connections being those of Fig. 11, thecut-off relay 3 is initially actuated by current from generator (Jrthrough winding 6; but as soon as armature 8 disengages anvil 74 currentwill flow from battery C of Fig. 8 through winding 7, tip contactpiecesof the spring-jack and plug and strand 13 to the office-return, causingthe complete actuation of the relay to remove the normal ground fromlimb 2 to short-circuit winding 6 and to short-circuit the winding ofrelay 4, thus preventing the display of calling-signal and providing anunobstructed path for ringing-current over liinbsl and 2. After therestoration of the ringing-key the further operation is similar to thatdescribed when answering a subscriber and will be clearlyunderstood.

The structure of Fig. 9 dilfers from those of the preceding figures inthat the windings of relay 3 are arranged concentrically and in that thenormallyshort-circuited winding7 is seriallyincluded in the line-limbafter the actuation of the cut-off relay and in other respects whichwill appear from this description. It is adapted for association withthe cord-circuit of Fig. 3 and operates as follows: The subscriber Acalls in the usual manner, completing a circuit of battery C throughrelay 4, armature 8, anvil 74, limbs 1 and 2, and impedance 71 to thereturn side of the battery, thus energizing relay 4 and lighting thecalling-lamp 5. Upon the insertion of the answering-plug P current willflow from battery C of Fig. 3 through relay 32, strand 12, plug and jackcontacts, winding 6 of relay 3, armature 8, anvil 74, limbs 1 and 2, andimpedance 71. This current will energize relay 3, extinguishing lamp 5by opening its local circuit at armature 9 and anvil 77. Upon thedisengagement of armature 8 from anvil 74 the current through relay 32will then flow through both windings of the relay 3, and current ofbattery O of Fig. 9 will continue to flow through relay 4 and winding 7,and upon the engagement of armature 8 with anvil 76 winding 6 becomesshort-circuited, the relay then being energized by current flowingthrough relays 32 and 4, through winding 7, and thence through limbs 1and 2 and impedance 71 to the oflice-return. Under this condition itwill be seen that while winding 7 is serially included in the line-limbit presents no objectionable interference to voice-currents, for thereason that its associated concentric winding 6 is short-circuited. Itwill also be seen that upon the insertion of an answering or a callingplug-relay 30 or 36 of the cord-circuit of Fig. 3 will be energized bycurrent flowing from battery 0 of that figure through strand 14 or 15 ofthe cord-circuit, the correspond ing contact-pieces of the plugandspring-jack and impedance 71 to the'return side of the battery, thuscontrolling the local circuit of the supervisory lamps and theconnection of relay 33 to strand 13 in the manner previously describedfor this cord-circuit. The insertion of a connecting-plug into aspringjack raises the potential of the sleeve or testing contact, andthe busy test is secured in the well-known manner. In considering theoperation of the apparatus when calling a subscriber it will beunderstood that the battery D and resistance 43 (shown in Fig. 3) wouldbe unnecessary and therefore omitted when this cord-circuit is used incombination with the line structure of Fig. 9. Upon the actuation of theringingkey current will flow through strand 13, winding 6, causing apartial or complete energization of the relay, and then through winding7 and'limbs 1 and 2 of the line to the return side of the generator, thepartial or complete energization of relay 3 preventing the display oflamp-signal 5, which might otherwise occur through an energization ofrelay 4, due to the connection of the ringing-generator G to theline-limb. Upon the restoration of the ringing-key the switchingmechanism of relay 3 returns to its normal position; but when thesubscriber removes his receiver current flowing through relays 32 and 4over the line-limbs will cause the initial and complete actuation ofrelay 3, as upon the insertion of an answering-plug.

Figs. 10 and 11 illustrate a line-circuit 3,1? rangement withappropriate cord connecting apparatus diifering from that of thepreceding figures in that the windings of both relays are associatedwith the tip side of the line-circuit and operates as follows: Whensubscriber A calls, the circuit of battery C is completed through anvil74, armature 8, relay 4, limbs 1 and 2, armature 9, and anvil 77. Uponthe insertion of an answering-plug P the relay 3 is initially actuatedby current from battery (J through anvil 74, armature 8, winding 7,strand 12, and relay 30. Upon the disengagement of armature 8 from anvil74 current will flow through winding 6 as well, and upon the engagementof armature 8 with anvil 76 and anvil 78 the relay will be entirelyenergized by current through winding 6,winding 7 will be short-circuitedby means of anvil 76, and relay 4 will be short-circuited by means ofanvil 78. At the same time armature 9 has disengaged anvil 77 andengaged anvil 75, thus breaking the normal ground of limb 2 andcompleting the circuit of limb 2 to the sleeve contact-pieces of thespringjack and plug, thence through strand 14 and relay 32. Theshort-circuiting of relay 4 causes the extinguishment of line-lamp 5,and current will be furnished to the substation transmitter throughwinding 6 and relay 32, while the circuit of the supervisory lamp willbe controlled at relay 30 by means of current flowing through this samewinding 6. The sleeve-contact or testing terminal of the spring-jack being normally disconnected and being connected to earth or ofiice returnupon the insertion of a plug, the manner of securing a busy test will beunderstood without further description. WVhen ringing a subscriber,relay 3 is energized by current from battery C flowing first throughanvil 74, armature 8, and winding 7, to strand 13, and the oflice-returnassociated with the generator circuit, subsequently flowing throughwinding 6 and 7, and finally through winding 6, armature 8, and anvil76, thus preventing the false illumination of signal-lamp 5 andcompleting the circuit of limb 2 through armature 9 and anvil 75 to thesleeve-terminal of the spring-jacks. After the restoration of theringing-key the operation of the line and cord circuit apparatus issimilar to that described during the use of the answering-plug and needsno further description.

WVhile various separate batteries C, C, C and 1) are indicated in theseveral drawings, it will be understood that these may be one and thesame battery, and also that the several grounds shown are or may be theofficereturn associated with the grounded side of the central battery.

In its broader phases my invention contemplates, first, a structure inwhich the display of the calling-signal is prevented by means of anelectromagnet having two windings, one normally short-circuited, butadapted to be brought into circuit with the line when the short-circuitis removed, and the other normally included in that portion of theline-circuit extending to the spring-jack and adapted to be excludedtherefrom, together with means whereby the connection of cordcircuitapparatus to the spring-jack energizes the electromagnet, and mechanismactuated by such energization adapted to remove the short-circuit, toexclude the said other winding, and to destroy the substation control ofthe calling-signal. Secondly, my invention contemplates the use in atwo-wire centralbattery telephone-exchange system of a normal earthconnection substantially devoid of resistance and impedance from thatline-limb con nected with the testing-terminal,and therefore adapted toprevent extraneous currents in the linelimb from altering the electricalcondition of said terminal, in association with means whereby theconnection of the cordcircuit apparatus with a spring-jack of the linecauses the removal of this normal earth connection.

\Vherever the phrase effective difference in electrical potential oreffective difference in potential is employed in the following claims,it is to be understood as meaning a difference of potential sufficientto cause a flow of current adapted to operate the testreceivinginstrument or operators testing instrument.

It will be understood by those skilled in the art that variousmodifications of my invention may be made diifering from thoseillustrated without departing from its spirit, and I therefore do notlimit myself to the precise structures shown and described; but

I claim 1. In atelephone-exchange system, the combination with atelephone-line connecting a substation with the central office andprovided with a plurality of switching-terminals thereat, a source ofcurrent at the central ofiice, a testing-contact for each of saidswitching-terminals, an operators testing instrument provided with atesting-terminal having normally no effective difi erence in potentialfrom that of the normal potential of the said testing contacts, a magnetand an associated line-signal normally under the control of thesubscriber, an electromagnet having two energizing-windings the firstwinding being normally short-circuited and the second winding beingnormally included in circuit with one limb of the line, means under thecontrol of the operator for causing the energization of theelectromagnet and switching mechanism associated with said electromagnctadapted upon its energization to remove the said second winding from thedirect line-circuit.

2. In a telephone-exchange system, the combination with a telephone-lineconnecting a substation withthe central office and provided thereat witha plurality of switching-terminals, a source of current at the centraloffice, a testing-contact for each of said switchingterminals, anoperators testing-terminal having normally no effective difference inelectrical potential from that of the normal potential of the saidtestingcontaets, a test-receiving instrument adapted to respond to aneffective difl'erence of potential between the said testing-terminal andtesting-contacts produced through the establishment of a connection withsaid line, a magnet and an associated line-signal normally under thecontrol of the subscriber, an electromagnet having twoenergizing-windings the first winding being normally short-circuited andthe second winding being normally connected with one limb of the line ina circuit not under control of the subscriber, means under control ofthe operator for causing the energization of the electrornagnet andswitching mechanismassociated with said electromagnet adapted upon itsenergization to include the said first winding in branch circuit of theline.

3. In a telephone-exchange system, the combination with a telephone-lineconnecting a substation with the central oflice and provided thereatwith a plurality of switching-terminals, a source of current at thecentral office, a testing-contact for each of said switchingterminals,an operators testing-terminal having normally no effective difierence inelectrical potential from that of the normal potential of the saidtesting-contacts, a test-receiv' inginstrument adapted to respond to aneffective difference of potential between the said testing-terminal andtesting-contacts produced through the establishment of a connection withsaid line, a magnet and an associated linesignal normally under thecontrol of the subscriber, an electromagnet having twoenergizing-windings the first winding being normally short-circuited andthe second winding being normally included in circuit with one limb ofthe line, means under the control of the operator for causing theenergization of the electromagnet and switching mechanism associatedwith said electromagnet adapted upon its energization to remove the saidsecond winding from the direct line-circuit and to include the sai firstwinding in branch circuit of the line. A

4. In a telephone-exchange system, the combination with a telephone;line connecting a substation with the central office and provided with aplurality of switching-terminals thereat, a source of current at thecentral office, a testing-contact for each of said switching-terminals,an operators testing instrument provided with a testing-terminal havingnormally no effective difference in potential from that of the normalpotential of the said testingcontacts, a magnet and an associatedline-signal normally under the control of the subscriber, anelectromagnet having two energizing-windings the first winding beingnormally short-circuited and the second winding being normally includedin circuit with one limb of the line, means under control of theoperator for causing the energization of the clectromagnet, switchingmechanism associated with said electromagnet adapted upon itsenergization to remove the said second winding from the directline-circuit and to include the said first winding in branch circuit ofthe line, and switching mechanism adapted to destroy the substationcontrol of the line-signal.

5. In a telephone-exchange system, the combination with a telephone-lineconnecting a substation with the central office and provided thereatwith a plurality of switching-terminals, a source of current at thecentral ofiice, a testing-contact for each of said switchingterminals,an operators testing-terminal having normally no effective difference inelectrical potential from that of the normal potential of the saidtesting-contacts, a test-re- .ceiving instrument adapted to respond toan effective difference of potential between the said testing-terminaland testing-contacts produced through the establishment of a connectionwith said line, a magnet and an associated line-signal normally underthe control of the subscriber, an electromagnet having twoenergizing-windings the first winding being normally short-circuited andthe second winding being normally included in direct circuit of the linebetween the source of current and the sWitching-terminals, means undercontrol of the operator for causing the energization of theelectromagnet and switching mechanism associated with said electromaguetadapted upon its energization to remove the said second winding from thedirect line-circuit.

6. In a telephone-exchange system, the combination with a telephone-lineconnecting a substation with the central offiee and provided with aplurality of switching-terminals thereat, a source of current at thecentral otfice, a testing-contact for each of said switching-terminals,an operators testing instrument provided with a testing-terminal havingnormally no effective difference in potential from that of the normalpotential of the said testingcontacts, a magnet and an associatedline-signal normally under the control of the subscriber, anelectromagnet having two energizing-windings the first winding beingnormally short-circuited and the second winding being normally connectedwith the line be tween alinelimb and the switching-terminals, meansunder control of the operator for causing the energization of theelectromagnet and switching mechanism associated with said electromagnetadapted upon its energization to include the said first winding inbranch circuit of the line.

7 In a telephone-exchange system, the combination with a telephone-lineconnecting a substation with the central ofiice and provided thereatwith a plurality of switching-terminals, a source of current at thecentral ohice, a testing-contact for each of said switchingterminals, anoperators testing-terminal haviug normally no effective dilference inelectrical potential from that of the normal potential of the saidtesting-contacts, a test-receiving instrument adapted to respond to anefiective difference of potential between the said testing-terminal andtesting-contacts produced through the establishment of a connection withsaid line, a magnet and anassociated line-signal normally under thecontrol of the subscriber, an electromagnet having twoenergizing-windings the first winding being normally short-cireuited andthe second winding being normallyincluded in direct circuit of the linebetween the source of current and the switching-terminals, means undercontrol of the operator for causing the energization of theelectromagnet and switching mechanism associated with said electromagnetadapted upon its energization to remove the said secondfrom the directline-circuit and to include the said first winding in branch circuit ofthe line.

8. In a telephone-exchange system, the combination with a telephone-lineconnecting a substation with the central oflice and provided with aplurality of switching-terminals thereat, a source of current at thecentral ofiice, a testing-contact for each of said switching-terminals,an operators testing instrument provided with a testing-terminal havingnormally no eflective difference in potential from that of the normalpotential of the said testing-contacts, a magnet and an associatedline-signal normally under the control of the subscriber, anclectromagnet having two energizing-windings the first winding beingnormally shortcircuited andthe second winding being normally included indirect circuit of theline between the source of current and theswitching-terminals, means under control of the operator for causing theenergization of the electromagnet, switching mechanism associated withsaid electromagnet adapted upon its energization to remove the saidsecond winding from the direct line-circuit and to include the saidfirst winding in branch circuit of the line, and switching mechanismadapted to destroy the substation control of the line-signal.

9. In a telephone-exchange system, the combination with a telephone-lineconnecting a substation with the central ofiice and provided thereatwith a plurality of switching-terminals, a source of current at thecentral office, a testingcontact for each of said switching-terminals,an operators testing-terminal having normally no effective difference inelectrical potential from that of the normal potential of the saidtesting-contacts, a testreceiving instrument adapted to respond to aneffective difference of potential between the said testing-terminal andtesting-contacts produced through the establishment of a connection withsaid line, a magnet and an associated line-signal normally under thecontrol of the subscriber, an electromagnet having twoenergizing-windings the first winding being normally short-circuited andthe second winding being normally included in that portion of theline-circuit extending to the switching-terminals, means under controlof the operator for causing the energization of the electromagnet andswitching mechanism associated with said electromagnet adapted upon itsenergization to remove the said second winding from the directline-circuit.

10. In a telephone-exchange system, the combination with atelephone-line connecting a substation with the central ofiice andprovided with a plurality of switching-terminals thereat normally notconnected to said line for conversation, a source of current at thecentral office, a testing-contact for each of said switching-terminals,an operators testing instrument provided with a testing-terminal havingnormally no efiective ditference in potential from that of the normalpotential of the said testing-contacts, a magnet and an associatedline-signal normally under the control of the subscriber, anelectromagnet having two energizing-windings the first winding beingnormally short-circuited and the second Winding being normally connectedbetween a line-limb and the switching-terminals, means under control ofthe operator for causing the energization of the electromagnet andswitching mechanism associated with said electromagnet adapted upon itsenergization to include the said first winding in branch circuit of theline and complete the conversational connection of theswitching-terminals to the line.

11. In a telephone-exchange system, the

' combination with a telephone-line connecting a substation with thecentral oflice and provided thereat with a plurality ofswitchingterminals, a source of current at the central office, atesting-contact for each of said switching-terminals, an operatorstesting-terminal having normally no efi'ective dilference in electricalpotential from that 'of the normal potential of the saidtesting-contacts, a test-receiving instrument adapted to respond to anefi'ective difference of potential between the said testing-terminal andtesting-contacts produced through the establishment of a connection withsaid line, a magnet and an associated line-signal normally under thecontrol of the subscriber, an electromagnet having twoenergizing-windings the first winding being normally short-circuited andthe second winding being normally included in that portion of theline-circuit extending to the switchingterminals, means under control ofthe operator for causing the energization of the electromagnet andswitching mechanism associated with said electromagnet adapted upon itsenergization to remove the said second winding from the directline-circuit and to include the said first winding in branch circuit ofthe line.

12. In a telephone-exchange system, the combination with atelephone-line connecting a substation with the central oflice andprovided with a plurality of switching-terminals thereat, a source ofcurrent at the central oflice, a testingcontact for each of saidswitchingterminals, an operators testing instrument provided with atesting-terminal having normally no effective difference in potentialfrom that of the normal potential of the said testing-contacts, a magnetand an associated linesignal normally under the control of thesubscriber, an electromagnet having two energizing-windings the firstwinding being normally short-circuited and the second winding beingnormally included in that portion of the line-circuit extending to theswitching-terminals, means under control of the operator. for causingthe energization of the electromagnet, switching mechanism associatedwith said electromagnet adapted upon its energization to remove the saidsecond winding from the direct line-circuit and to include the saidfirst winding in branch circuit of the line, and switching mechanismadapted to destroy the substation control of the line-signal.

18. In a telephone-exchange system, the combination with atelephone-line connecting a substation with the central office andprovided thereat with a plurality of switchingterminals normally notconnected to said line for conversation, a source of current at thecentral ofiice, a testing-contact for each of said switching-terminals,an operators testing-terminal having normally no effective difference inelectrical potential from that of the normal potential of the saidtesting-contacts,

a test-receiving instrument adapted to respond to an elfectivediii'erence of potential between the said testing-terminal andtesting-contacts produced through the establishment of a connection withsaid line, a magnet and an associated line-signal normally controlledfrom the substation, .au electromagnet having a normally short-circuitedwinding in bridge of the line with said source of current and a secondwinding normally connecting the line with the switching-terminal, acord-circuit terminating in a connectingplug, means whereby theconnection of the plug with the switching-terminal causes theenergization of the electromagnet and switching mechanism controlled bythe electromagnet adapted upon its energization to remove the shortcircuit from the first-mentioned winding and complete the conversationalconnection of the switching-terminals to the line.

14. In a telephone-exchange system, the combination with atelephone-line connecting a substation with the central oflice andprovided with a plurality of switching-terminals thereat, a source ofcurrent at the central oflice, a testing contact for each of aidswitching-terminals, an operators testing instrument provided with atesting-terminal having normally no effective diiference in potentialfrom that of the normal potential of the said testing-contacts, a magnetand an associated line-signal, an electromagnet having a normallyshort-circuited winding in bridge of the line with said source ofcurrent and a second winding in the direct circuit of the lineintermediate of the bridged connection and the switching-terminal, acord -circuit terminating in a connectingplug, means whereby theconnection of the plug with the switchingterminal causes theenergization of the electroi'nagnet and switching mechanism controlledby the electromagnet adapted upon its energization to remove the saidsecond winding from the direct circuitof the line.

15. In a telephone-exchange system, the combination with atelephone-line connecting a substation with the central oflice andprovided thereat with a plurality of switching terminals, a source ofcurrent at the central oflice, a testing-contact for each of saidswitching-terminals, an operators testingterminal having normally noeflective difference in electrical potential from that of the normalpotential of the said testing-contacts, a test-receiving instrumentadapted to respond to an eflective difference of potential between thesaid testing-terminal and testing-contacts produced through theestablishment of a connection with said line, a magnet and an associatedline-signal, an electromagnet having a normally short-circuited windingin bridge of the line with said source of current and a second windingin the direct circuit of the line intermediate of the bridged connectionand the switching-terminals, a cord-circuit terminating in aconnecting-plug, means whereby the connection of the plug with theswitching terminal causes the energization of the electromagnet andswitching mechanism controlled by the electromagnet adapted upon itsenergization to remove the short circuit from the first-mentionedwinding and to remove the said second winding from the direct circuitoi' the line.

16. In a telephone-exchange system, the combination with atelephone-line connecting a substation with the central oflice andprovided with a plurality of switching-terminals thereat, a source ofcurrent at the central oftice, a testing-contact for each of saidswitching-terminals, an operators testing instrument provided with atesting-terminal having normally no effective difierence in potentialfrom that of the normal potential of the-said testing-contacts, a magnetand an associated line-signal normally under the control of thesubscriber, an electromagnet having a nor mally short-circuited windingin bridge of the line with said source of current and a second windingin the direct circuit of the line intermediate of the bridged connectionand the switchingterminals, a cord-circuit terminating in aconnecting-plug, means whereby the connection of the plug with theswitchingterminal causes the energization of the electromagnet,switching mechanism controlled by the electromagnet adapted upon itsenergization to remove the short circuit from the first-mentionedwinding and to remove the said second winding from the direct circuit ofthe line, and switching mechanism adapted to destroy the substationcontrol of the linesignal.

17. In a telephone-exchange system, the combination with a telephoneline connecting a substation with the central otlice and provided with aplurality of switching-terminals thereat, a source of current at thecentral office, a testing-contact for each of said switching-terminals,an operators testing instrument provided with a testing-terminal havingnormally no ciiective difference in potential from that of the normalpotential of the said testing-contacts, a magnet and an associatedline-signal, an electromagnet having a winding in bridge of the linewith said source of current and a second winding normally connecting theline with the switching-terminal,

a low-resistance connection at the central of:

tice from said source of current to that linelimb associated with thefirst-mentioned winding, means under control of the operator for causingthe energization of the electromagnet and switching mechanism controlledby the electromagnet adapted upon its energization to interrupt saidlow-resistance connection.

18. In a telephone-exchange system, the combination with atelephone-line connecting a substation with the central office and pro;

vided thereat with a plurality of switchingterminals, a source ofcurrent at the central oflice, a magnet and an associated line-signal, atesting-contact for each of said switchingterminals, an operatorstcstingterminal having normally no effective difference in electricalpotential from that of the normal potential of the saidtesting-contacts, a test-receiving instrument adapted to respond to aneffective difference of potential between the said testing-terminal andtesting-contacts produced through the establishment of a connection withsaid line, an electromagnet having awinding in bridge of the line withsaid source of current and a second winding in direct circuit of theline intermediate of the bridged connection and the switching-terminals,alowresistance connection at the central oflice from said source ofcurrent to that line-limb associated with the first-mentioned Winding,means under control of the operator for causing the energization of theelectromagnet and switching mechanism controlled by the electromagnetadapted upon its energization to interrupt said low-resistanceconnection and to remove the said second winding from the direct circuitof the line.

19. In a telephone-exchange system, the combination With atelephone-line connecting a substation with the central oflice andprovided with a plurality of switching-terminals thereat, a source ofcurrent at the central ofiice, a testing-contact for each of saidswitching-terminals, an operators testing instrument provided with atesting-terminal having normally no etl'ective diiference in potentialfrom that of the normal potential of the said testing-contacts, a magnetand an associated line-signal normally under the control of thesubscriber, an electromagnet having a winding in bridge of the line withsaid source of current and a second winding in the direct circuit of theline intermediate of the bridged connection and the sWitching-terminals,a lowresistance connection at thecentral ofifice from said source'ofcurrent to that line-limb associated with the first-mentioned winding,means under control of the operator for causing the energization of theelectromagnet and sWitcl ing mechanism controlled by the electromagnetadapted upon its energization to interrupt the said low-resistanceconnection and to remove the said second winding from the direct circuitof the line, and switching mechanism adapted to destroy the substationcontrol of the line-signal.

20. In a telephone-exchange system, the combination with atelephone-line connecting a substation with the central oifice andprovided with a plurality of switching-terminals thereat, a source ofcurrent at the central ofiice, a testing-contact for each of saidswitching-terminals, an operators testing instrument provided Withatesting-terminal having normally no eflective difference in potentialfrom that of the normal potential of the said testing-contacts, a magnetand an associated line-signal, an electromagnet having'its Winding incircuit with a talking-contact of said switching-terminals and source ofcurrent, said winding being connected to a line-limb from itsintermediate point, switching mechanism controlled by said electromagnetadapted to alternately complete a circuit of low resistance from saidintermediate point to either end of said Winding and means under controlof the operator for controlling the position of said switchingmechanism.

21. In a telephone-exchange system, the combination with atelephone-line connecting a substation with the central office andprovided there-at with a plurality of switchingterminals, a source ofcurrent at the central oflice, a testing-contact for each of saidswitching-terminals, an operators testing-terminal having normally noeffective difference in electrical potential from that of the normalpotential of the said testing-contacts, a testreceiving instrumentadapted to respond to an effective difference of potential between thesaid testing-terminal and testing-contacts produced through theestablishment of a connection with said line, a magnet and an associatedline signal, an electromagnet having its Winding in circuit with atalking-contact of said switching-terminals and source of current, saidwinding being connected to a line-limb from its intermediate point,switching mechanism controlled by said electromagnet adapted to normallyshort-circuit one portion of said winding and when actuated to removesaid short circuit and means under control of the operator forcontrolling the position of said switching mechanism.

22. In a telephone-exchange system, the combination with atelephone-line connecting a substation with the central oifice andprovided With a plurality of switching-terminals thereat, a source ofcurrent at the central office, a testing-contact for each of saidswitching-terminals, an operators testing instrument provided with atesting-terminal having normally no efl 'ective difference in potentialfrom that of the normal potential of the said testing-contacts, a magnetand an associated line-signal, an electromagnet having its winding incircuit with a talking-contact of said switching-terminals and source ofcurrent, said Winding being connected to a line-limb from itsintermediate point, switching mechanism controlled by said electromagnetadapted to normally short-circuit one portion of said Winding and whenactuated to remove said short circuit and to short-circuit the otherportion of said winding and means under control of the operator forcontrolling the position of said switching mechanism.

23. In a telephone-exchange system, the combination with atelephone-line connecting a substation with the central office andprovided thereat with a plurality of switchingterminals, a source ofcurrent at the central office, a testing-contact for each of saidswitching-terminals, an operators testing-terminal having normally noeffective difference in elec- .trical potential from that of the normalpotential of the said testing-contacts, a test-receiving instrumentadapted to respond to an efl'ective difference of potential between thesaid testing-terminal and testing-contacts produced through theestablishment of a connection with said line, a magnet and an associatedline-signal, an electromagnet having its winding in circuit with atalking-contact of said switching-terminals and source of current, saidwinding being connected to a linelimb from its intermediate point,switching mechanism controlled by said electromagnet adapted to normallyshort-circuit one portion of said winding and when actuated to removesaid short circuit, to short-circuit the other portion of said windingand to destroy the substation control of the line-signal, and meansunder control of the operator for controlling the position of saidswitching mechanism.

21. In a telephone-exchange system, the combination of a telephone-lineconnecting a substation with the central office, switchingterminals forthe line having testing and talking contact-pieces normally connected toits two limbs, a source of current at the central oifice, a magnet andan associated line-signal, an electromagnet having twoenergizing-windings the first winding being normally shortcircuited andthe second winding normally connecting said terminals with one limb ofthe line, testing means for determining the busy or idle condition ofthe line, a normal earth connection for that line-limb associated withthe testing contact-pieces adapted to prevent extraneous currents frominterfering with the normal operation ofsaid testing means, acordcircuitadapted to make connection with said sWitching-terminals and to completea circuit of said source including said second winding whereby theelectromagnet is energized and switching mechanism associated with saidelectromagnet adapted upon its energization to interrupt said normalearth connection.

25. In a telephone-exchange system, the combination of a telephone-lineconnecting a substation with the central ofiice, switchingterminals forthe line having testing and talking contact-pieces normally connected toits two limbs, a source of current at the central office, a magnet andan associated line-signal,

an electromagnet having two energizing-windings the [irst winding beingnormally shortcircuited and the second winding being normall y includedin. circuit with one limb of the line, testing means for determining theidle or busy condition of the line, a normal earth connectionsubstantially devoid of resistance and impedance for that line-limbassociated with the testing contact-pieces adapted to prevent extraneouscurrents from interfering with the normal operation of said testingmeans, a cord-circuit adapted to make connection with saidswitching-terminals and to complete a circuit of said source includingsaid second winding whereby the electromagnet is energized and switchingmechanism associated with said electromagnet adapted upon itsenergization to interrupt said normal earth connection and toremove thesaid second winding from the direct line-circuit.

26. In a telephone-exchange system, the combination of a telephone-lineconnecting a substation with the central office, switchingterminals forthe line having testing and talking contact-pieces normally connected toits two limbs, a source of current at the central office, a magnet andan associated line-signal, an electromagnethaving twoenergizing-windings the first winding being normally shortcircuited andthe second winding being normall y interposed between said terminals andone limb of the line, testing means for determining the idle or busycondition of the line, a normal earth connection for that line-limbassociated with the testing contactpieces adapted to prevent extraneouscurrents from interfering with the normal operation of said testingmeans, a cord-circuit adapted to make connection with saidswitching-terminals and to complete a circuit of said source includingsaid second winding whereby the electromagnet is energized and switchingmechanism associated with said electromagnet adapted upon itsenergization to interrupt said normal earth connection and to includethe said first winding in branch circuit of the line.

27. In a telephone-exchange system, the combination of a telephone-lineconnecting a substation with the central ofiice, switchingterminals forthe line having testing and talking contact-pieces normally connected toits two limbs, a source of current at the central office', a magnet andan associated line-signal, an electromagnet having twoenergizing-windings the first winding being normally shortcircuited andthe second winding being normally included in circuit with one limb ofthe line, testing means for determining the busy or idle condition-ofthe line, a normal earth connection for that line-limb associated withthe testing contact-pieces adapted to prevent extraneous currents frominterfering with the normal operation of said testing means, acordcircuit adapted to make connection with said switching-terminals andto complete a circuit of said source including said second windingwhereby the electromagnet is energized and switching mechanism.associated with said electromagnet adapted upon its energization tointerrupt said normal earth connection, to remove the said secondwinding from the direct line-circuit and to include the said firstwinding in branch circuit of the line.

28. In a telephone-exchange system, the

combination of a telephone-line connecting a l circuited and the secondwinding being nor- Substation with the central office,switchingterminals fortheline having testing and talking contact-piecesnormally connected to its two limbs, a source of current at the centralofiice, a magnet and an associated line-signal normally underthe'control of the subscriber. an electromagnethaving two energizingwind- -ings the first winding being normallyshort-circuited and thesecond winding being normally included in circuit with one limb of theline,

testing means for determining the idle or busy condition of the line, anormal earth connection for that line-limb associated with the testingcontact-pieces adapted to prevent extraneous currents from interferingwith the normal operation of said testing means, a cord-circuit adaptedto make connection with said switching-terminals and to complete acircuit of said source including said second winding whereby theelectromagnet is energized and switching mechanism associated with saidelectromagnet adapted upon its energization to interrupt said normalearth connection, to remove said second winding from the directline-circuit, to include the said first winding in branch circuit of theline and to destroy the substation control of the line-signal.

29. In a telephone-exchange system, the combination of a telephone-lineconnecting a substation with the central ofiice, switchingterminals fortheline having testing and talking contact-pieces normally connected toits two limbs, a source of current at the central office, a magnet andan associated line-signal, an electromagnet having twoenergizing-windings the first winding being normally shortcircuited andthe second winding being normally included in circuit between thelineand said switching-terminals, testing means for determining the busyor idle condition of the line, a normal earth connection for thatlinelimb associated with the testing contactpieces, adapted to preventextraneous currents from interfering with the normal operation of saidtesting means, a cord -circuit adapted to make connection with saidswitching-terminals and to complete a circuit of said source includingsaid second winding whereby the electromagnet is energized and switchingmechanism associated with said electromagnet adapted upon itsenergization to interrupt said normal earth connection and complete theconversational connection of said contact-pieces to the line.

30. In a telephone-exchange system, the combination of a telephone-lineconnecting a substation with the central office, switchingterminals forthe line having testing and talking contact-pieces normally connected toits two limbs, a source of current at the central office, a magnet andan associated line-signal, an electromagnet having twoenergizing-windings the first winding being normally shortmeans, acord-circuit adapted to make connec mally included in direct circuit ofthe line between the source of current and the switch ing-terminals,testing means for determining the idle or busy condition of the line, anormal earth connection for that line-limb associated with the testingcontact-pieces, adapted to prevent extraneous currents from interferingwith the normal operation of said testing means, a cord-circuit adaptedto make connection with said switching-terminals and to complete acircuit of said source including said second winding whereby theelectromagnet is energized and switching mechanism associated with saidelectromagnet adapted upon its energization to interrupt said normalearth connection and to remove the said second winding from the directline-circuit.

31. In a telephone-exchange system, the combination with atelephone-line connecting a substation with the central ofiicc,switchingterminals for the line having testing and talkingcontact-pieces normally connected to its two limbs, a source of currentat the central oflice, a magnet and an associated line-signal, anelectromagn et having two energizing-windings the first winding beingnormally shortcircuited and the second winding being normally includedin circuit between the line and said switching-terminals, testing meansfor determining the busy or idle condition of the line, a normal earthconnection for that linelimb associated with the testing contact-pieces,adapted to prevent extraneous currents from interfering with the normaloperation of said testing means, a cord-circuit adapted to makeconnection with the said switching-terminals and to complete a circuitof said source including said second winding whereby the electromagnetis energized and switching mechanism associated with said electromagnetadapted upon its energization to interrupt said normal earth connection,to include the said first winding in branch circuit of the line andcomplete the conversational connection of said contactpieces to theline.

32. In a telephone-exchange system, the combination of a telephone-lineconnecting a substation with the central office, switchingterminals forthe line having testing and talking contact-pieces normally connected toits two limbs, a source of current at the central oflice, a magnet andan associated line-signal, an electromagnet having twoenergizing-windings the first winding being normally shortcircuited andthe second winding being normally included in direct circuit of the linebetween the source of current and the switchingterminals, testing meansfor determining the busy or idle condition of the line, a normal earthconnection for that line-limb associated with the testingcontact-pieces, adapted to prevent extraneous currents from interferingwith the normal operation of said testing tion with saidswitching-terminals and to complete a circuit of said source includingsaid second winding whereby the electromagnet is energized and switchingmechanism associated with said electromagnet adapted upon itsenergization to interrupt said normal earth connection, to remove thesaid second winding from the direct line-circuit and to include the saidfirst winding in branch circuit of the line.

33. In a telephone-exchange system, the combination of a telephone-lineconnecting a substation with the central office, switchingterminals forthe line having testing and talking contact-pieces normally connected toits two limbs, a source of current at the central office, a magnet andan associated line-signal normally under the control of the subscriber,an electromagn et having two energizing-windings the first winding beingnormally shortcircuited and the second winding being normally includedin direct circuit of the line between the source of current and theswitchingterminals, testing means for determining the idle or busycondition of the line, a normal earth connection for that line-limbassociated with the testing contact-pieces adapted to prevent extraneouscurrents from interfering with the normal operation of said testingmeans, a cord-circuit adapted to make connection with saidswitching-terminals and to complete a circuit of said source includingsaid second winding whereby the electromagnet is energized and switchingmechanism associated with said electromagnet adapted upon itsenergization to interrupt said normal earth connection, to remove saidsecond winding from the direct line-circuit, to include the said firstwinding in branch circuit of the line and to destroy the substationcontrol of the linesignal.

34;. In a telephone-exchange system, the combination of a telephone-lineconnecting a substation with the central office, switchingtermi'nals forthe line having testing and talking contact-pieces normally connected toits two limbs, a source of current at the central office, a magnet andan associated line-signal, an electromagnet having twoenergizing-windings the first winding being normally shortcircuited andthe second winding being normally included intermediate of theline-circuit and the sWitching-terminals,testing means for determiningthe idle or busy condition of the line, a normal earth connection forthat line-limb associated with the testing contactpieces adapted toprevent extraneous currents from interfering with the normal operationof said testing means, a cord-circuit adapted to make connection withsaid switching-termin als and to complete a circuit of said sourceincluding said second winding whereby the electromagnet is energized andswitching mechanism associated with said electromagnet adapted upon itsenergization to interrupt said normal earth connection.

35. In a telephone-exchange system, the combination of a telephone-lineconnecting a substation with the central office, switchingterminals forthe line having testing and talking contact-pieces normally connected toits two limbs, a source of current at the central ofiice, a magnet andan associated line-signal, an electromagnet having twoenergizing-windings the first winding being normally shortcircuited andthe second winding being normally included in that portion of theline-cir-' cuit extending to the switching-terminals, testing means fordetermining the idle or busy condition of the line, a normal earthconnection for that line-limb associated with the testing contact-piecesadapted to prevent extraneous currents from interfering with the normaloperation of said testing means; a cord-circuit adapted to makeconnection with said switchingterminals and to complete a circuit ofsaid source including said second winding whereby the electromagnet isenergized and switching mechanism associated with said electromagnetadapted upon its energization to interrupt said normal earth connectionand to remove the said second winding from the direct line-circuit. w

86. In a telephone-exchange system, the combination of a telephone-lineconnectinga substation with the central office, switchingterminals forthe line having testing and talking contact-pieces normally connected toits two limbs, a source of current at the central ofiice, a magnet andan associated line-signal,

an electromagnet having two energizing-windings the first winding beingnormally shortcircuited and the second Winding being normally includedintermediate of the line-circuit and the switching-terminals, testingmeans for determining the idle or busy condition of the line, a normalearth connection for that linelimb associated with the testingcontact-pieces adapted to prevent extraneous currents from interferingwith the normal operation of said testing means, a-cord-circuit adaptedto make connection with said switching-terminals and to complete acircuit of said source including said second winding whereby theelectromagnet is energized and switching mechanism associated with saidelectromagnet adapted.

upon its energization to interrupt said normal earth connection and toinclude the said. first winding in branch circuit of the line.

37. In a telephone-exchange system, the combination of a telephone-lineconnecting a substation with the central office, switchingterminals forthe line having testing and tall:- ing contact-pieces normally connectedto its two limbs, a source of current at the central office, amagnet andan associated line-signal, an electromagnet having twoenergizing-windings the first winding being normally shortcircuited andthe second winding being normally included in that portion of theline-circuit extending to the switching-terminals, testing means fordetermining the busy or idle condition of the line, a normal earthconnection for that line-limb associated with the testing contact-pieces adapted to prevent extrane ous currents from interferingwith the normal operation of said testing means, a cord-circuit adaptedto make connection with said switching-terminals and to completeacircuit of said source including said second winding whereby theelectromagnet is energized and switching mechanism associated with saidelectromagnet adapted upon its energization to interrupt said normalearth connection, to remove the said second winding from the directline-circuit and to include the said first Winding in branch circuit ofthe line.

38. In a telephone-exchange system, the combination of a telephone-lineconnecting a substation with the central office, switchingterminals forthe line having testing and tall:- ing contact-pieces normally connectedto its two limbs, a source of current at the central ofiice, a magnetand an associated line-signal normally under the control of thesubscriber, an electromagnet having two energizing-windings the firstwinding being normally shortcircuited and the second winding beingnormally included in that portion of the line-circuit extending to theswitching-terminals, testing means for determining the busy or idlecondition of the line, a normal earth connection for that line-limbassociated with the testing contact-pieces adapted to pre ventextraneous currents from interfering with the normal operation of saidtesting means, a cord-circuit adapted to make connection with saidswitching-terminals and to complete a circuit of said source includingsaid second winding whereby the electromagnet is energized and switchingmechanism associated with said electromagnet adapted upon itsenergization to interrupt said normal earth connection, to remove saidsecond winding from the direct linecircuit, .to include the said firstwinding in branch circuit of the line and to destroy the substationcontrol of the line-signal.

In witness whereof I hereunto subscribe my name this 11th day ofNovember, A. D. 190a.

HARRY Gr. WEBSTER.

\Vitnesses:

L. D. KELLoee, A. H. DYSON.

